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HOXA1 is a member of an evolutionarily conserved family of genes called homeobox transcription factors. These transcription factors regulate the expression of many genes that ultimately guide the development of the embryonic body plan across the anterior-posterior axis (head to feet).
Hox genes were first discovered in fruit flies and recognized to be very important for proper segmentation of the insect and placement of body parts. It was discovered soon afterwards that members of this gene family in fruit flies were present in the genomes of all mammals and vertebrates. The importance of these findings resulted in the 1995 Nobel Prize in physiology and medicine shared by three investigators for their discoveries concerning the "genetic control of early embryonic development":
http://nobelprize.org/medicine/laureates/1995/press.html
HOX genes are found in four paralogous gene clusters (A, B, C, D) in humans, each on a different chromosome and each containing up to 11 genes. The order of HOX genes within each cluster corresponds to their temporal and spatial expression patterns during development. Generally, genes at the 3' ends of each cluster are expressed early in anterior regions (head) of the human embryo, whereas genes at the 5' ends of each cluster are expressed later in posterior regions (hands and feet). This is known as the colinearity principle of HOX gene expression.
HOXA1 is the most 3' HOX gene in cluster "A" and the first HOX gene expressed in mammals. It is also among the first genes expressed in the central nervous system, and accordingly, plays a critical role in brain and head development. HOXA1 is primarily responsible for segmenting the embryonic hindbrain into seven transient compartments called rhombomeres. Each rhombomere has a distinct set of molecular and cellular properties that is necessary for organizing groups of immature neurons into functional networks that will eventually mediate important functions such as breathing, eye movement, and mastication.
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